Some conventional television games need to play for a long time period, i.e., it is difficult for them to be finished within one play. In such games, the state of progress at the time when playing is stopped can be saved (stored) in a back-up file. When the game is restarted, the player can play the game from the same state of progress.
In many cases, a plurality of back-up files to be saved are prepared. Thus, the player can select any of the states of progress when the game is restarted. The back-up file can be also made during the playing. For example, if the player wants to restart the game from a scene in which he is interested, the state of progress corresponding to the scene can be saved into a back-up file, and he can restart the game from the same scene by reading out the back-up file any time. As long as the content of the back-up file remains, the game can be repeatedly restarted from the same state.
FIG. 1 shows relationships between back-up files and states of progress and between saving and loading in a game. In this example, the saving is conducted in the order of progress states A, B and C as shown by (1) to (3) in FIG. 1. When the progress state B is, as shown by (4) in FIG. 1, loaded, the game can be restarted from the progress state B.
In FIG. 1, a progress state D is rewritten in the back-up file where the progress state C was saved ((5)). At this time, the progress state C is erased from the back-up file, and the progress states A, B and D are left in the respective back-up files. Though the player can restart the game from any of the progress states A, B and D at this time, he cannot restart it from the progress state C. Anyway, since the progress states in the back-up files are independent of one another, each of the progress states can be always reproduced to go back to the time when it is saved.
However, the conventional back-up method for the television game cannot be suitably adapted to a new type of television game. The reasons are as follows.
There is a television game in which real time (actual time ticked away by a clock) is incorporated into the game story to give a kind of virtual reality. Though such a game can also employ the conventional back-up method, a problem occurs in the case that there exists a character whose state varies in the process of real time. For example, there exists a pet character which needs a proper food to be given within a time period. Now, when the game is repeatedly played by the player, a plurality of back-up files, each of which has different data regarding the food supplying condition of the pet, are saved. When the player restarts to play the game while reading out data of one of the back-up files after several hours, the time period may be passed. Thus, his expectation that the pet is still alive may be disappointed. This is because a plurality of back-up files which are perfectly independent of one another are saved.